Clinical specular microscopy. I. Optical principles.

The clinical specular microscope yields a corneal endothelial image. Depending on the slit width of the illumination source, a typical endothelial photomicrograph contains three or four distinct zones. The appearance of the boundary between the endothelial cell pattern and the adjacent dark zone, called the dark boundary, reflects the configuration of the endothelial cell-aqueous humor interface and provides important information about the posterior corneal surface.